Two part grommet with hard plastic locking prongs

ABSTRACT

A grommet for sealing a cable to a panel opening includes a hard plastic part formed with curved locking prongs projecting at an angle from the perimeter of a main piece is molded to a soft elastomeric second part having a boot portion to receive the cable and a perimeter flange. The prongs lock to the panel upon being fully inserted into the panel opening.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional Serial No. 60/409,266, filed Sep. 9, 2002.

BACKGROUND OF THE INVENTION

[0002] This invention concerns grommets installed in panel holes to seal to elongated elements such as electrical or control cables passed through the panel holes and also are used to seal panel access holes. Grommets are pushed into the panel hole until a capturing feature passes through the hole and then springs out to capture the grommet against a sealing flange pressed against the opposite entry side of the panel. Grommets have in the past been constructed of soft rubber or other elastomers to insure an effective sealing pressure on the cable and panel surfaces.

[0003] However, the lack of stiffness has allowed the grommet to be dislodged from the panel by pressure exerted by the cable, particularly when the cable extends at a severe angle to grommet. There have heretofore been developed “dual durometer” grommets which have hard plastic portions embedded in a softer sealing elastomer. The panel mating portions have still been constructed of soft material such that dislodgement resistance is still not satisfactory in all applications.

[0004] Other problems include the necessity of exerting a high force on the grommet to install the grommet, and the difficulty assemblers have in determining when a grommet is fully seated.

[0005] It is an object of the present invention to provide a grommet which has a high resistance to dislodgment from the panel hole in which it is installed while still effectively sealing to a cable passed through the grommet and the panel hole.

[0006] It is another object of the invention to provide a grommet which is easily installed and provides an indication to the assembler when proper seating of the grommet has been achieved.

SUMMARY OF THE INVENTION

[0007] The above recited objects and other objects which will become apparent upon a reading of the following specification and claims are achieved by a two part grommet comprised of a first part molded from a suitable hard plastic having a very generally annular main body defining a central opening. A series of spaced apart resiliently deflectable prongs are integrally formed around the perimeter of the main body projecting back at an angle over the main body, having a radiused curve outer.

[0008] A second portion of a suitable soft elastomer is overmolded to the first part, having an outer flange portion projecting past the first part for sealing against one side of the panel. A boot portion is disposed within the central opening of the main body and has a tubular feature designed to sealingly grip the cable passed therethrough. The second part has portions bonded to the inside of the prongs as well as the spaces between the prongs, and a relief space is provided between the prongs and the main body to insure ready deflectability of the prongs.

[0009] A sealing flange extends radially from a projecting portion of the second part which projecting part is sufficiently long to allow the prongs to snap out over the opposite side of the panel when fully inserted, providing an audible indication when the grommet has been fully seated.

[0010] The curved outer shape of the prongs minimizes the insertion force required by increasing the angle of the contact force as the prongs are advanced into the panel hole.

DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a plan view of a grommet according to the invention.

[0012]FIG. 2 is a new of a longitudinal section through the grommet shown in FIG. 1 taken along the lines 2-2 in FIG. 5.

[0013]FIG. 3 is a view of the transverse section through the grommet of FIG. 1 taken along the line 3-3.

[0014]FIG. 4 is an enlarged fragmentary sectional view of an outer portion of the grommet shown in FIG. 1.

[0015]FIG. 4A is a fragmentary view of the section shown in FIG. 4 installed in a panel hole.

[0016]FIG. 5 is a reverse plan view of the grommet shown in FIG. 1.

[0017]FIG. 6 is a plan view of the hard plastic part of the grommet shown in FIG. 1.

[0018]FIG. 7 is a perspective view of the grommet shown in FIG. 1 installed in a panel shown in fragmentary form.

[0019]FIG. 8 is a reverse perspective view of the installed grommet section in FIG. 7.

DETAILED DESCRIPTION

[0020] In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.

[0021] Referring to the drawings, a grommet 10 according to the present invention is shown in FIG. 1, and is formed of two molded parts, a hard plastic part 12, and a soft elastomeric part 14, which may be molded in a two shot process, so as to be melt bonded together. The materials are preferable compatible so as to produce the melt bonding. A suitable compatible material for the hard plastic part 12 includes polypropylene (glass fiber reinforced 8-10%) and for the soft elastomeric part 14 SANTOPRENE™.

[0022] Other candidates for the hard plastic include nylon, polyolefin, ABS, and other crystalline thermoplastics, and thermo set materials such as vinyl ester and polyester. Other materials for the soft part include isoprene, natural rubber, butyl, EPDM, nitrile, neoprene, polyacrylate, silicone, epichlorohydrin, plastomers and other synthetic elastomers.

[0023] The hard plastic first part 12 is shown by itself in FIG. 6, and includes a generally elongated annular main piece 18 defining a central opening 16. The elongated annular main piece 18 defines a wall angled in towards the central opening 16 and has pairs of side projecting locking prongs 20 integrally formed therewith and angled over the annular piece 18 to form a vee shaped intermediate space. The side locking prongs 20 are curved along a radius for a purpose to be described below.

[0024] An end locking prong 22 is integrally formed at each end of the piece 18, and have a similarly curved radiused shape.

[0025] Scalloped clearance spacer 24 are formed centered into each side and at each end to accommodate sharply angled cables (not shown).

[0026] The locking prongs 20, 22 are sized to be resiliently compressed as the grommet 10 is inserted into a panel hole 26 (FIG. 4A). The outside of the prongs 20, 22 are curved to a selected radius. This shape has been found to lower the insertion force required since the angle of the force vector acting on the prongs 20, 22 as a result of contact with the edge of the panel hole decreases, as the prongs are advanced and compressed during insertion, with respect to the plane of the hole. This progressive decrease in that angle reduces the peak force required to compress the prongs as compared to a simple straight chamfer shaped prong, since the contact angle remains constant.

[0027] The prong radius chosen is a function of the radius chosen in a function of two variables. The first variable is the “normal angle” which is the angle of the normal reaction force to the plane of the opening at initial contact of the grommet prongs 20, 22 with the edge of the panel hole 26. The normal angle was designed to be greater than 60°. This was to maximize the compressive effect and minimize the insertion resistance effect of the two vectors of the normal force. The second variable is the amount of required overlap or interference for retention purposes. This overlap also affect insertion efforts if the material needs to compress too much.

[0028] The oval hole for a particular grommet measured 63.5 mm×31.75 mm. That grommet measured 66.1 mm×33 mm, giving 2.6 mm of overlap lengthwise and 1.25 mm of overlap across the width. With these given overlaps and the normal angle target, a lead in surface with a radius of 10.2 mm was developed to satisfy all requirements for this part. The normal contact angle is greater than 60° at contact and increases to 90° as the part is inserted. The insertion efforts for this grommet are significantly less than a part with a prong shape having a chamfered lead in, i.e., are reduced by at least half.

[0029] The soft elastomeric part 14 of the grommet 10 is molded to the hard plastic part 12, and includes a central boot lying within the central opening 16 of the hard plastic part 12. The boot includes tubular neck 30 sized to sealingly grip the cable to be passed through the grommet 10, annular ribs 32 aiding in gripping and sealing to the cable.

[0030] The soft elastomeric part 14 is also formed with a flange 34 extending radially outward around the perimeter of the part 14. The flange 34 is normally molded to be flared towards the side of the panel 36 from which the grommet 10 is inserted so as to be flattened out against the panel surface A as the grommet 10 is fully seated in the panel opening 26 (FIG. 4A). The shape creates a greater sealing pressure exerted by the flange 34.

[0031] The soft elastomeric part 14 extends into the vee shaped space between the prongs 20, 22 and main piece 18 creating a bonded connection between parts 12, 14.

[0032] A vee shaped in section space 38 is also formed into the soft elastomeric part 14 to maintain flexibility of the prongs 20, 22, while bracing the same against buckling after the grommet 10 is fully seated in the panel hole 26 (FIG. 4A). The thick wall 40 extends along the spaces between the prongs 20, 22.

[0033] After the prongs 20, 22 have been moved past the far edge of the panel hole 26, the prongs 20, 22 snap back out, emitting and audible sound, and providing a tactile feedback to the installer, that the grommet 10 is fully installed. The bracing of the prongs 20, 22 strengthens the same against buckling to provide a strong resistance to pull out.

[0034] The distance D between the inside surface of the flange 34 and the tip of the prongs 20, 22 is selected to insure that the prongs 20, 22 will snap out when the grommet 10 is fully seated. This also insures panel hole edge contact only with the soft second part 14, which enables an additional area of sealing in addition to the flange. 

1. A grommet for sealing an elongated element passing through a hole in a panel, said grommet comprising: a first part constructed of a hard plastic material and including a main piece defining a central opening; a series of integral prongs protruding from a perimeter of said main piece, said prongs each having an outer surface inclined with respect to a plane of said central opening; a second part constructed of a soft elastomeric material, said second part attached to said first part and having a boot portion lying within said central opening defined by main piece of said first part, said boot portion having an opening configured to sealingly engage said elongated element; said prongs resiliently deflectable inwardly upon insertion of said grommet into said panel opening from one side of said panel to allow advance of said grommet into said panel hole.
 2. The grommet according to claim 1 wherein said inclined outer surface of said prongs is curved.
 3. The grommet according to claim 1 wherein said main piece is angled outwardly from said central opening and said prongs are angled back in an opposite direction therefrom to form a vee shaped space therebetween allowing said inward resilient deflection of said prongs.
 4. The grommet according to claim 3 wherein said second part includes a portion bonded to each of said prongs and said main piece portions of said first part adjacent to said vee shaped space.
 5. The grommet according to claim 4 wherein said portion of said second part is formed with a vee shaped space aligned with but spaced from said vee shaped space between said prongs, and said main piece accommodating said inward resilient deflection of said prongs.
 6. The grommet according to claim 1 wherein said second part has a perimeter flange extending radially outward beyond said first part prongs and adapted to engage one side of said panel upon advance of said prongs through said panel hole.
 7. The grommet according to claim 7 wherein said prongs have ends terminating a predetermined distance from said flange sufficient to accommodate a thickness of said panel whereby said prongs can move out to lock against a side of said panel opposite said one side.
 8. The grommet according to claim 7 wherein said second part has a portion extending within and past said prong ends to said flange portion thereof.
 9. The grommet according to claim 1 wherein said second part has a portion underlying each prong and in contact therewith.
 10. The grommet according to claim 1 wherein said grommet has an elongated shape defining two sides and two ends, and wherein two prongs are located on each side, and one prong is located on each end.
 11. The grommet according to claim 1 wherein said first part main piece is formed with clearance scallops for accommodating a sharply angle elongated element.
 12. The grommet according to claim 1 wherein said first part is formed of glass filled polypropylene and said second part is formed of SANTOPRENE.
 13. A method of forming a grommet for sealing a cable to a hole in a panel comprising the steps of: molding a hard plastic first part having a main piece defining a central opening and having a series of resilient deflectable prongs projecting radially from said main piece and inclined in one direction from said main piece; molding a second soft elastomeric part having a boot portion formed with an opening sealingly receiving said cable; and fixing said second part to said first part with said boot portion lying within said central opening of said first part.
 14. The method according to claim 13 wherein said step of fixing said first part to said second part includes the step of molding said parts together.
 15. The method according to claim 13 wherein in said step of molding said second part, a flange is formed about a perimeter of said second part extending radially outwardly beyond said first part prongs and said panel hole when said prongs are inserted in said panel hole.
 16. The method according to claim 15 wherein in said step of molding said first part, a vee shaped space is formed between the inside of each prong and said main piece accommodating inward deflection of said prongs.
 17. The method according to claim 16 wherein said step of molding said second part, a portion thereof underlying and bonded to each prong is formed.
 18. The method according to claim 17 wherein in said step of molding said second part a vee shaped space is formed in said second part aligned and spaced from said vee shaped space formed by said prongs. 